Our research focus begins with developing a molecular picture of the specific interactions of HIV elements with human target cell proteins to define which host factors are required to sustain a productive viral infection. An immediate objective of these studies is to provide new targets for interventive drug therapies. In addition, using what we learn from these molecular studies, we are endeavoring to develop new animal models to study the interaction of HIV with the immune system of the host. Comprehensive immunological studies of the interaction of HIV with the host immune system have been hindered by the lack of an adequate animal model that sustains a pathogenic HIV infection. To accelerate our understanding of how HIV destroys the host immune system and develop new strategies to bolster the immune system to fend off this insidious attack, we are attempting to genetically manipulate mice to make them permissive to HIV infection. To enable efficient HIV-1 replication in transgenic mice, we have initiated two complementary sets of studies. The first approach requires further genetic manipulation of the mouse to make it a more suitable host for the virus. Our second, parallel approach relies on manipulation of the HIV-1 genome to make it more suitable for replication in murine cells. This includes protocols to adapt HIV-1 for replication in murine cells through selective pressure in vitro. To develop a basis for our manipulation of mice, we are examining the nature of the additional impediments to HIV replication in murine cells to determine (1) how they effect virus production and (2) whether these blocks are due to a lack of positive factors in murine cells or to the presence of negative factors. Our analyses have revealed so far that the remaining blocks to replication appear to be posttranscriptional, occuring prior to viral maturation. The dominance or recessive nature of these blocks is currently being ascertained. If murine cells are found to lack positive cofactors typically expressed in human cells, the human cofactors will then be introduced as transgenes into mice already transgenic for human CD4, CCR5, and cyclin T1. If negative murine factors are identified, they will be interfered with posttranscriptionally, genetically ablated from HIV target cells, or in vitro selected HIV variants will be used that are less susceptible to their prohibitive effects. In fact, we are also performing prospective screenings for positive cofactors that would promote steps of virus replication actively blocked in murine cells by negative factors. These studies on positive and negative cofactors will be useful not only in developing a mouse susceptible to HIV infection but in understanding how HIV interacts with the host cell. Indeed, a better molecular understanding of HIV replication has the potential to provide new targets for disrupting infection of the virus in vivo. Given that lentiviruses have colonized many mammalian species, and early-stage restrictions to HIV replication in murine cells have been obviated once human cofactors were identified, we are confident that continued selective genetic manipulation of the mouse and possibly the virus will yield a murine model to study HIV infection and immunopathogenesis.